The present invention relates to a plastic lens, in particular a pickup lens which is a component of an optical head for optical disks, magnetooptical disks and the like.
The drive unit of optical disks, magnetooptical disks and the like (which are hereunder collectively referred to as "optical disks") is equipped with an optical head for reading out the information recorded on the optical disks.
The optical head has a pickup lens (objective lens) fixed on a lens holder in the moving part of an actuator and when an electric current is applied to the coil of the actuator, the moving part is driven in two independent directions, one being parallel to the optical axis of the pickup lens and the other being along the radius of the optical disk, so as to perform focusing and tracking control.
The pickup lens is typically manufactured by injection molding of plastic materials. The gate or channel through which a molten plastic material is injected into a mold is located on a lateral side of a cavity (molding space) which conforms to the shape of the pickup lens to be molded and, hence, the produced pickup lens has a corresponding projection (gate portion) formed as an integral part of the periphery.